Invasion by the non-native earthworm Amynthas agrestis (Oligochaeta: Megascolecidae)
Snyder, Bruce Allen
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Over the past several decades, invasive species have become one of the largest issues in the field of ecology. Invasive earthworms have received much attention, especially in northern North America, where native earthworms were extirpated by Pleistocene glaciations and the more recent earthworm invasions have altered Northern Forests significantly. These invasions were primarily by European species and invasions elsewhere in the continent by other earthworm taxa have received less attention. We studied the impacts of invasion by Asian earthworms in the genus Amynthas in a field study and two laboratory studies. Amynthas agrestis invasion in the Great Smoky Mountains National Park was found to be a dynamic process on monthly time scale. This invasion altered soils by decreasing the depth of partially decomposed organic horizons and increasing soil aggregation. A significant decrease in millipede abundance and species richness was also associated with the invasion, which suggested competitive interactions between the epigeic earthworm and epigeic millipedes. To further examine this interaction, two microcosm studies were performed. The first study used C enriched Red Oak and Eastern Hemlock litter to assess millipede (Pseudopolydesmus erasus) and earthworm (Amynthas corticis) food preference. Negative effects of earthworms on millipede C assimilation were observed as was a mitigation of earthworms’ impacts on soil aggregation by millipedes. A. corticis caused significant soil aggregation throughout microcosms and increased respiration rates relative to millipede and control treatments. The second microcosm experiment examined millipedes’ (Sigmoria ainsliei) and earthworms’ (Amynthas agrestis) reliance on fresh versus partially decomposed litter as a food resource and whether there was direct competition for these resources. These taxa were found to compete for partially decomposed material and millipedes relied on this resource for survival. The results of these studies suggest that Asian earthworm invasion in the southern Appalachian Mountains poses a threat to the millipede species endemic to this region. To assist land managers in conservation of this vital resource, a preliminary checklist of millipedes of the Great Smoky Mountains National Park has been compiled. This assembles the knowledge of millipede diversity and species distributions within the Park for the first time.